The present invention pertains to a method and apparatus for the control of pollution present in waste gases, and more particularly, is directed to the removal of sulfur oxides from the waste gases.
Because of the recent emphasis on the control of pollution into the atmosphere, particularly from the burning of fuels and the like, attempts have been made to switch to the use of low sulfur fuels since it is well known that the presence of sulfur constitutes a major source of pollution. Another approach, however, to the pollution problem, and particularly to that associated with the burning of fuel in large power plants, is to provide an economical technique for absorbing the noxious waste gases and converting them so as to remove substantially their sulfur dioxide content. Some of the proposals that have been made may be appreciated by reference to the following U.S. Pat. Nos. 3,501,897; 3,436,192; 3,524,720; 3,454,356; 3,508,868; 3,345,125; 3,363,401; 2,992,895; and 3,795,732. As is particularly pointed out in the first listed patent, the primary consideration when a particular system is to be adopted for controlling pollution is the cost of that system, both with respect to initial capital investment and the operating costs involved.
The present invention is concerned with achieving a desulfurization objective within reasonable costs and yet being able efficiently to reduce the sulfur dioxide content of the effluent to new strict standards. Thus, the technique of the present invention makes possible with great economy the production of tail gases which contain sulfur dioxide at levels as low as 100 p.p.m.
It is a primary object of the present invention to provide an economical pollution control system that will reduce sulfur dioxide content in waste gases to approximately 100 p.p.m.
Another subordinate or ancillary object is to efficiently convert the remaining sulfur dioxide, which is still present as a result of already practiced conversion techniques, to sulfur trioxide thereby to obtain an increment of sulfuric acid as a byproduct of the over-all process.
The above and other objects are achieved by a primary feature of the present invention which resides in the utilization of ozone generation and scrubbing techniques as an efficient and economical conversion means and, in a specific implementation, by judiciously combining ozone generation and scrubbing with established techniques so as to significantly lower the levels of sulfur dioxide already obtained by those established techniques. Thus, additional conversion of sulfur dioxide to sulfur trioxide is readily achieved by contact of the effluent with ozone; thereafter, the increased resulting amount of sulfur trioxide is removed by means of scrubbing techniques to produce a significant increment of sulfuric acid.
The present invention proceeds upon the recognition that although a simple ozone generation technique would, if applied to waste gases having a high level sulfur dioxide content (2000 p.p.m.), tend to be extremely costly, such a technique can be effectively exploited in cases where such sulfur dioxide content is about 300 p.p.m. However, in the typical case of waste gases emanating from sulfur fuel-burning plants, these consist of such a great quantity of carbon monoxide and other unburned hydrocarbons that to apply ozone generation directly would still be inefficient and uneconomical. On the other hand, if conditions are such that a relatively low sulfur dioxide content exists (approximately 300 p.p.m.) and a low hydrocarbon content is also present, then ozone generation can be utilized directly and immediately, whereby the desired results of the invention can be achieved.
Broadly considered, the present invention improves upon currently available pollution abatement techniques by contacting the gases resulting from conventional operations, which gases still contain fairly high levels of sulfur dioxide, with ozone so as efficiently to convert substantially all of the remaining sulfur dioxide therein to sulfur trioxide; and thereafter further scrubbing the gas mixture so as to absorb the thus converted sulfur trioxide.
In the context under normal consideration, that is, in connection with waste gases emanating from a power plant or the like, the present invention improves upon conventional desulfurization processes by introducing a catalytic burning step for the waste gases containing the sulfur dioxide immediately as these gases emanate from the discharge end of a combustion furnace or the like. Following the catalytic burning step, conventional steps are performed, and then the improvement step of ozone generation is applied at that state when the gases have had their sulfur dioxide content reduced sufficiently; that is, at a stage when that content is down to about 300 p.p.m.
It will be appreciated, as the description proceeds, that the principle of the invention can be variously applied in connection with a variety of industrial processes so as to realize the particular abatement of sulfur dioxide pollutants.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.